Technological development and increased demand for mobile equipment have led to a sharp increase in the demand for secondary batteries as energy sources. Among these secondary batteries, lithium secondary batteries having high energy density and driving voltage, long lifespan and low self-discharge are commercially available and widely used.
In addition, in recent years, increased interest in environmental issues has brought about a great deal of research associated with electric vehicles (EVs) and hybrid electric vehicles (HEVs) as substitutes for vehicles, such as gasoline vehicles and diesel vehicles, using fossil fuels which are major causes of air pollution. Nickel metal hydride (Ni-MH) secondary batteries are generally used as power sources of electric vehicles (EVs), hybrid electric vehicles (HEVs) and the like. However, research associated with use of lithium secondary batteries having high energy density, high discharge voltage and power stability is actively underway and some of such lithium secondary batteries are commercially available.
A lithium secondary battery has a structure in which a non-aqueous electrolyte comprising a lithium salt is impregnated into an electrode assembly comprising a cathode and an anode, each comprising an active material coated on a current collector, and a porous separator interposed therebetween.
Recently, a carbon-based material is generally used as an anode for lithium secondary batteries. However, the carbon-based material has a potential of 0V which is lower than lithium, thus disadvantageously inducing reduction of an electrolyte and causing generation of gas. In order to solve these problems, lithium titanium oxide (LTO) having a relatively high potential is also used as an anode active material.
However, LTO may cause generation of a great amount of hydrogen gas during activation and charge/discharge, leading to deterioration in safety of secondary batteries.
Accordingly, there is an increasing need for methods capable of ultimately solving these problems.